syzbot

rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
rcu: 	Tasks blocked on level-0 rcu_node (CPUs 0-1): P8838/2:b..l
	(detected by 1, t=10502 jiffies, g=59901, q=120 ncpus=2)
task:syz.1.1039      state:R  running task     stack:23776 pid:8838  ppid:4267   flags:0x00004002
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5244 [inline]
 __schedule+0x10ec/0x40b0 kernel/sched/core.c:6561
 preempt_schedule_irq+0xb1/0x150 kernel/sched/core.c:6873
 irqentry_exit+0x63/0x70 kernel/entry/common.c:439
 asm_sysvec_apic_timer_interrupt+0x16/0x20 arch/x86/include/asm/idtentry.h:691
RIP: 0010:__rcu_read_unlock+0x2/0xd0 kernel/rcu/tree_plugin.h:419
Code: 11 ff 03 8b 03 3d 00 00 00 40 7d 02 5b c3 0f 0b eb fa 89 d9 80 e1 07 80 c1 03 38 c1 7c e3 48 89 df e8 42 28 65 00 eb d9 41 57 <41> 56 41 55 41 54 53 49 bf 00 00 00 00 00 fc ff df 65 48 8b 3d 15
RSP: 0018:ffffc90003746ff8 EFLAGS: 00000293
RAX: ffffffff83f415f0 RBX: 1ffff1100f56f881 RCX: ffff88807d5dbb80
RDX: 0000000000000000 RSI: ffffffff8adef740 RDI: ffffffff8adef700
RBP: dffffc0000000000 R08: dffffc0000000000 R09: fffffbfff1c3ed56
R10: fffffbfff1c3ed56 R11: 1ffffffff1c3ed55 R12: ffff88802d4fac00
R13: ffff888142bd9110 R14: ffff88807ab7c408 R15: ffff888142bd9000
 rcu_read_unlock include/linux/rcupdate.h:823 [inline]
 blkg_tryget_closest block/blk-cgroup.c:1900 [inline]
 bio_associate_blkg_from_css+0xb81/0xc00 block/blk-cgroup.c:1926
 bio_associate_blkg+0x129/0x1c0 block/blk-cgroup.c:1954
 bio_init block/bio.c:260 [inline]
 bio_alloc_bioset+0x61d/0x1190 block/bio.c:545
 bio_alloc include/linux/bio.h:427 [inline]
 submit_bh_wbc+0x266/0x4d0 fs/buffer.c:2682
 __block_write_full_page+0x88c/0x1680 fs/buffer.c:1792
 __writepage+0x63/0x130 mm/page-writeback.c:2447
 write_cache_pages+0x85b/0x1400 mm/page-writeback.c:2382
 generic_writepages+0xf7/0x160 mm/page-writeback.c:2473
 do_writepages+0x3b7/0x610 mm/page-writeback.c:2491
 filemap_fdatawrite_wbc+0x11e/0x180 mm/filemap.c:388
 __filemap_fdatawrite_range mm/filemap.c:421 [inline]
 filemap_write_and_wait_range+0x10b/0x1d0 mm/filemap.c:674
 filemap_write_and_wait include/linux/pagemap.h:60 [inline]
 sync_blockdev block/bdev.c:198 [inline]
 blkdev_put+0xea/0x710 block/bdev.c:911
 blkdev_close+0x51/0x80 block/fops.c:514
 __fput+0x22c/0x920 fs/file_table.c:320
 task_work_run+0x1ca/0x250 kernel/task_work.c:203
 exit_task_work include/linux/task_work.h:39 [inline]
 do_exit+0x93e/0x2400 kernel/exit.c:880
 do_group_exit+0x217/0x2d0 kernel/exit.c:1022
 get_signal+0x1272/0x1350 kernel/signal.c:2871
 arch_do_signal_or_restart+0xb7/0x1240 arch/x86/kernel/signal.c:871
 exit_to_user_mode_loop+0x70/0x110 kernel/entry/common.c:174
 exit_to_user_mode_prepare+0xee/0x180 kernel/entry/common.c:210
 __syscall_exit_to_user_mode_work kernel/entry/common.c:292 [inline]
 syscall_exit_to_user_mode+0x16/0x40 kernel/entry/common.c:303
 do_syscall_64+0x58/0xa0 arch/x86/entry/common.c:87
 entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7fb46378f6c9
RSP: 002b:00007fb464688038 EFLAGS: 00000246 ORIG_RAX: 000000000000012b
RAX: 0000000000010106 RBX: 00007fb4639e6090 RCX: 00007fb46378f6c9
RDX: 0000000000010106 RSI: 00002000000000c0 RDI: 0000000000000003
RBP: 00007fb463811f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000002 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fb4639e6128 R14: 00007fb4639e6090 R15: 00007ffcbb2c54f8
 </TASK>
rcu: rcu_preempt kthread starved for 9528 jiffies! g59901 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x0 ->cpu=1
rcu: 	Unless rcu_preempt kthread gets sufficient CPU time, OOM is now expected behavior.
rcu: RCU grace-period kthread stack dump:
task:rcu_preempt     state:R  running task     stack:27840 pid:16    ppid:2      flags:0x00004000
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5244 [inline]
 __schedule+0x10ec/0x40b0 kernel/sched/core.c:6561
 schedule+0xb9/0x180 kernel/sched/core.c:6637
 schedule_timeout+0x15c/0x280 kernel/time/timer.c:2167
 rcu_gp_fqs_loop+0x2f2/0x1310 kernel/rcu/tree.c:1706
 rcu_gp_kthread+0x95/0x380 kernel/rcu/tree.c:1905
 kthread+0x29d/0x330 kernel/kthread.c:376
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295
 </TASK>
rcu: Stack dump where RCU GP kthread last ran:
CPU: 1 PID: 0 Comm: swapper/1 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/02/2025
RIP: 0010:default_idle+0xb/0x10 arch/x86/kernel/process.c:742
Code: 48 89 df e8 b7 3b af f7 e9 4c ff ff ff e8 dd 07 f6 ff 00 00 cc cc 00 00 cc cc 00 00 cc cc 00 66 90 0f 00 2d 97 d4 64 00 fb f4 <c3> 0f 1f 40 00 41 57 41 56 53 49 be 00 00 00 00 00 fc ff df 65 48
RSP: 0018:ffffc90000177de8 EFLAGS: 000002c6
RAX: 16a0ab0901ceca00 RBX: ffffffff8a21ce97 RCX: 16a0ab0901ceca00
RDX: 0000000000000001 RSI: ffffffff8a8c0580 RDI: ffffffff8adef760
RBP: ffffc90000177f20 R08: dffffc0000000000 R09: ffffed10171e6afa
R10: ffffed10171e6afa R11: 1ffff110171e6af9 R12: 0000000000000001
R13: dffffc0000000000 R14: ffff88813fed9dc0 R15: 1ffffffff1c3ed96
FS:  0000000000000000(0000) GS:ffff8880b8f00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f6d0f0366c8 CR3: 00000000300ba000 CR4: 00000000003506e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 default_idle_call+0x84/0xc0 kernel/sched/idle.c:109
 cpuidle_idle_call kernel/sched/idle.c:191 [inline]
 do_idle+0x1fc/0x570 kernel/sched/idle.c:303
 cpu_startup_entry+0x3f/0x60 kernel/sched/idle.c:401
 start_secondary+0xe4/0xf0 arch/x86/kernel/smpboot.c:281
 secondary_startup_64_no_verify+0xcf/0xdb
 </TASK>